Electron discharge device



Feb. 27, 1940. ALD U 2,191,903

ELECTRON DISCHARGE DEVICE Filed Aug. 10, 1958 I 5 {0 Z /I 9 I II vvvv n -L 3 n 1 2 25 2e 22 23 l W4 '27 ,7 1.9 TLZU HT,

INVENTOR. WILLIAM HERBERTALDOUS ATTORNEY.

' Patented Feb. 27, 1940 7, 2,191,903 1 F 7 cinnamon mscnmosnsvrce William Herbert Aldous, Wembley, England, as-

signor to The MoYalve Company, Limited, a

British company Applicati gust 10, 1938, Serial No. 224,071,

' In Great Britain May 4, 1937 i 2 Claims. (01. 250 -17 The invention relatesto electron discharge de-= vices ofv the multi-grid'type and particularly suitable for frequency changing in superheterodyne receivers, the two frequencies to be intermodw 'lated beingapplied respectivelyto two different successive control grids.

' A tube of this kind has the usual-cathode and anode and a screen between the two control grids.

A second screening grid is usually placed between the anode and the control grid next to it. The sequence of electrodes is then '(1) cathode (2)" first grid first control grid, (3) second grid=first screening grid, (4) third "grill -second control grid, (5) fourth grid second screening grid, (6)

'15 anode In using such a so-called hexode the first and third grids are usually made negative to I the cathode, the second and fourth grids positive to the cathode. a

I In tubes with the electrodes arranged and connected in this, manner, some of the electrons passing through the "second grid are turned back by the third grid and-'may oscillate about the second grid. So long as the periodof the electrical oscillations applied to any grid is long com- 25, pared with the transit time of the electrons be! tween any two electrodes, electrons which have passed "the second' grid can'neverbe caught by the first grid, which is negative to the cathode But if this condition is not fulfilled, electrons j 30 after passing the second grid may receive energy from the high frequency field and may reach the first grid. They then produce damping in the input circuit connected tothe first grid, and the operation of the frequency changer is impaired in known manner.

The primary object of this invention is to prevent such impairment. The means adopted to prevent it do not introduce any serious disad vantages at low frequencies. The invention is not confined to tubesof the type specifiedadapted to beoperated at very high frequencies, and may be applied to tubes suitable for receiving broadcast- The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will be best understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 50 1 shows a schematic diagram of a tube made according to my invention and its associated circuit,

and Figure 2 shows almodification of the tube shown in Figure 1, and its associated circuit.

The general 'idea underlying the invention is 55 to cause the third grid to control, not the primary electrons ,frorn'the cathode, but secondary elec-'- trons produoedlby these primaries atthe second grid; These secondaries, when they leave the second grid, have a kinetic energy so low that any additional energy they may acquire-'from the high frequency field cannot make their kinetic" energy sufficient to'enable them' to r-eachthe first grid again} On the other hand, if the potential of the third grid isnot too different from that of the second grid (being preferably just more nega- 1 t'ive) the secondary electrons, when they reach the third grid, willhave' kinetic energies so small that they are easily controlled by it. The primary electrons, having a high kinetic energy in theneighbourhood of the third grid are not turned back by it, but proceed almost unafiectedtowards theanode. I According to the invention an' electron discharge device of the type specified includes at least one secondary emission grid, intervening be- 0 tween the first and second control grids, com posed of or coated with material having a coefiicient of secondary electron emissionsubstantially greater than that of any clean metal such as nickel, tungsten or molybdenum; Preferably its surface is one of those knownto have the highest coeifici'en'ts of secondary emission and used for the secondary'c'athodes of elec'tron'multi pliers, for example that produced by heating an oxidized metal in caesium vapor.

Instead of a single grid so coated between the control grids a series of grids each so coated may i be introduced, and in operation maintained each at a more positive potential thanthepreceding,

so that, in known manner, the number of secondary electrons is increased by the" impact of electrons from an earlier grid on a later grid.

The single secondary emission grid or the combination of grids in series must be such as to act in a known manner as a screening grid between the first and second control grid;

If, as is preferable, there is a screening grid between the second control grid and anode, it should be capable of being maintained at a higher :potential than the second grid, and therefore should not be connected within the tube to the second grid. For since the secondary electrons will not be accelerated materially, if at all, by the second control grid, they must receive their acceleration from the screening grid.

An acceleratinggrid may be interposed between the secondary emission grid(s) and the second control grid, and maintained in operation at a potential positive to both of them. The secondary electrons in the neighbourhood of the second control grid are then in a retarding field, as are the electrons controlled by the second control grid in the aforesaid hexode.

In the ordinary use of the hexode aforesaid, the cathode and the second control grid are often connected directly to the cathode and control grid of an oscillator tube, which is within the same envelope as the hexode and shares its cathode. -A tube according to the'invention may share its cathode with another tube adapted to act as an oscillator, but it is not possible to connect the second control grid to the control grid of the oscillator, since the second control grid must be substantially positive to the cathode; but the second control grid may be connected to the anode of the oscillator. Alternatively acondenser and grid leak coupling may be used.

-In thedrawing the tube made according to the I invention is used as a frequency changenand is along with a triode, serving as an oscillator supplying it, enclosed in a common envelope I, and share a common cathode 2. Thetube has the following electrodes in order: The cathode 2, i

the first control grid 3,. the screening grid 4 coated in known manner with material of high coefficient of secondary emission, the accelerating grid 5,-the second control'grid 6, the second 1 screening grid 7 (which may be connected within the tube, as shown, to the accelerating grid 5),

and the anode 8. The triode consists of cathode 2, control grid 9, and anode l0 joined directly to second control gridfi.

The input circuit comprising the coil ll and condenser I8 is connected between the cathode 2 and first control grid 3. The various voltages for the various grids are obtained by a Voltage divider arrangement comprising resistors 2l-22, 24-25 and by-passing condensers 23 and 26. The oscillator circuit comprises the coil II and v condensers I 2' I2, and a blocking condenser M used topermit high voltage to be applied to the anode ll] of the oscillator section of the tube.

The biasing resistors I3 and I9 and 29 serve to obtain'proper biases for the various electrodes.

Bypassing condensers 20 and 21 are used. The output circuit connected to the anode 8 comprises condenser 29 and primary of transformer l6 for supplying the intermediate frequency.

The modification of my invention in which the tube is provided with a plurality of grids between the control grid and accelerating grid and each t coated with emitting materialis shown'in Fig. 2.: These grids are grids 4, 4 and 4" and obtain their:

proper voltages from the divider resistor 30. The

arrangementis otherwise the same as in Fig; 1.

While I have indicated the preferred embo'dif ments of my invention of which I am'now aware, and have also indicated only one, specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which itis employed without jde-' parting from the scope of my invention as set forth in the appended claims.

What I claim as new is: Q 1. An electron discharge device for frequency changing and having a cathode, a first control grid, a plurality of successive grids coatedtw ith emitting material, an accelerating grid, a second control grid and an anode, and a grid and'a) my second anode directly adjacent and laterally of! an I said cathode and independent of theiother gridsand other anode for providing an oscillator sec-Q tion in the tube and a-connection between the 7 second anode and the secondcontrol grid.

t 2. An electron discharge device for frequency changing and having a cathode for emitting pri-' maryelectrons, a first control grid, agrid coated with emitting material for emitting secondary,

electrons when struck by primary electrons from said cathode, an accelerating grid, asecond cone trolgrid and an anode for receiving secondary electrons from the coated grid, a grid and a sec- 0nd anode directly adjacent and laterally of said cathode and independent of the other grids and other anode for providing an oscillator sec-.

tion in the tube, said second control being adapted to modulate said' secondary electrons fromsaid coatedgrid during operation of said. electron discharge device and a connection .be-

tween the oscillator anode and the second con-'- trol grid.

HERBERT ALDOUS; I v 

